They already exist, silly. They're called "house hippos" and are a common household animal in Canada and Eastern United States. Their nests are made of dryer lint, lost mittens and bits of string. They sleep 16 hours a day so they have to be extra soft.
Their diet consists of raisins, potato chips and the crumbs from peanut butter on toast.

oh, well, I saw it on TV some years ago, and I still can't forget about them. That's why I had to mention them in the first place on this forum. But I'm still angry that they show us such a wonderful creature to finally tell us they don't exist and now we have to put our best geneticists on it! I've been waiting for too long! I want an hippopotamice!